PURPOSES : In general, a high-performance concrete construction method is a method of loading mixed cement and other materials on a mobile mixer equipped with a concrete plant. However, the construction cost is high because the unit cost of the mixed cement is very high and the equipment usage fee of the mobile mixer is also high. To compensate for these drawbacks, a cellular spray concrete method was developed. This is a highly functional customized concrete construction method in which admixtures are added to high-flow concrete with cellular (air bubbles) added at the site and constructed through spraying. METHODS : Field workability evaluation using cellular concrete was carried out using a spray method in 2017 and an anti-foaming agent in 2018. The test construction section was set as a new road-pavement construction site. After construction, strength, durability characteristics, and void analysis were performed to compare the construction methods. The results of laboratory tests under optimal conditions were also compared to the on-field results. By comparing the indoor mixing and the on-field results, we analyzed whether there were any problems concerning the performance expression. The economic feasibility at the initial construction stage was analyzed by comparing the existing and the cellular concrete construction methods in terms of material cost and equipment usage fee. RESULTS : In the case of cellular spray concrete, construction through spraying is cumbersome, and the need to additionally use large equipment such as a pump car and compressor constitutes a disadvantage. However, the most relevant feature is that it can be constructed not only on the floor, but also on a slope. In the case of cellular concrete with an antifoaming agent, it was possible to quickly produce high-performance concrete using on-site remixing equipment. By supplying materials to the pouring surface using a conveyor, smooth construction and construction in narrow spaces were also possible. CONCLUSIONS : The cellular concrete method allows the immediate on-site production of high-performance concrete, and it is possible to selectively apply spray construction, antifoaming agent construction, etc.

PURPOSES : The purpose of this study is to analyze not only the strength but also the durability and abrasion resistance of concrete pavements as increasing the cases of domestic concrete pavement damage which do not meet the service years. METHODS: The bottom layer of a two-lift concrete pavement was paved with original Portland cement (OPC) with 20~23 cm thickness. On the other hand, the top-layer, which is directly exposed to the environment and vehicles, was paved with high-performance concrete (HPC) with 7~10 cm thickness. For the optimal mixed design of the top-layer material of a two-lift concrete pavement, silica fume and polymer powder were mixed. Furthermore, it analyzes abrasion resistance of concrete as follow‘ ASTM C 779’which is dressing wheel abrasion test method. RESULTS : As a result, abrasion resistance is improved with increasing the silica fume ratio. When the polymer powder is mixed, abrasion resistance of concrete is much improved. However, the effect of mixing ratio is not significant. It is very effective that adding both silica fume and polymer powder occur 20~40% of abrasion comparing with OPC variables. CONCLUSIONS : The concrete strength and durability increased with silica fume and polymer powder. In particular, it is significant increasing strength of polymer powder under the flexural strength. In the abrasion resistance side, it is also significant when the silica fume and polymer powder used together.

PURPOSES : This purpose of this study is to analyze the effect to autogenous shrinkage of the top-layer material of a two-lift concrete pavement mixing both silica fume and polymer powder. METHODS: The bottom-layer of a two-lift concrete pavement was paved with original portland cement (OPC) with a 20~23 cm thickness. Additionally, the top-layer which is directly exposed to the environment and vehicles was paved with a high-performance concrete (HPC) with a 7~10 cm thickness. These types of pavements can achieve a long service life by reducing joint damage and increasing the abrasion and scaling resistance. In order to integrate the different bottom and top layer materials, autogenous shrinkage tests were performed in this study according to the mixing ratio of silica fume and polymer powder, which are the admixture of the top-layer material. RESULTS: Autogenous shrinkage decreased when polymer powder was used in the mix. Contrary to this, autogenous shrinkage tended to rise with increasing silica fume content. However, the effects were not significant when small amounts of polymer powder were used (3% and 11%). CONCLUSIONS : The durability and compressive strength increase when silica fume is used in the mix. The flexural strength considerably increases and autogenous shrinkage of concrete decreases when polymer powder is used in the mix. As seen from above, the proper use of these materials improves not only durability, but also autogenous shrinkage, leading to better shrinkage crack control in the concrete.

단위 바인더량을 400과 420으로 결정하였으며, 잔골재율 58%, W/B를 38%로 결정하였다. 혼화재료의 경우 현장 투입을 위해 추가 첨가하는 개념으로 실리카퓸을 중량대비 3% 첨가, 라텍스를 5% 첨가 하였고, 속경성 혼화재료의 경우 10∼40% 까지 첨가하여 첨가량에 따른 강도를 확인 하고자 하였다. 표1은 실험에 사용된 배합표이다. 기본적으로 속경성 혼화재료의 혼입량이 증가할수록 강도는 점차 증가하는 것으로 나타났으나, 12시간 강도에서는 바인더량에 따라 강도 차이가 크지 않았다. 그러나 24시간 강도에서는 혼입률이 적은 변수(10∼20%)구간 보다 혼입률이 높은 변수(30∼40%)구간에서 강도 증진이 크게 나타났다. 그림1은 변수별 강도 시험 결과 이다.

현장재배합 장비 개념 현장재배합 장비는 트윈샤프트 믹서를 이용하여 현장에서 콘크리트에 기포, 속경성 혼화재료, 고분말 고내구성 혼화재료 등을 투입 한 뒤 빠르게 교반하여 혼입한 뒤 배출하는 방식으로, 대표적으로 배치식과 연속식 두 가지 방식이 있다. 장비개발 내용 본 연구를 통해 개발된 배치식 현장 재배합 장비는 버켓 컨베어를 이용하여 콘크리트를 0.5m3 트윈 샤프트 믹서에 공급하고, 기포 및 혼화재료를 투입하는 형태로 개발되었다. 5톤 차량에 상차하여 일체화 거동이 가능하며, 발전기가 내장되어 있어 버켓 컨베어, 믹서, 배출구 개폐 등이 자동으로 가능하다. 그림1은 개발된 현장재배합 장비 전경이다. 결 론 현장 재배합 장비는 일반 콘크리트를 저렴한 가격으로 현장에서 즉시 원하는 성질의 콘크리트로 전환할 수 있으나, 현재 배치식의 경우 시공 속도가 느리다는 단점이 있다. 향후 지속적인 개발을 통해 연속식 장비로 개선해야 할 필요가 있다.

배치플랜트에서 생산된 보통 레미콘을 현장으로 이송 후 펌프카로 압송 도중 기포와 고성능, 기능성, 속경성 혼합재료를 투입하여 재배합 하는데, 이 때 기포의 볼 베어링 효과를 이용해 혼합재료를 콘크리트 내에 고르게 분산시키게 되나 콘크리트에 다량의 공기가 존재함으로 강도를 크게 감소시키고 슬럼프를 크 게 증가시켜 원하는 작업성 범위를 벗어나게 되므로 공기압 스프레이 공법을 활용하여 공기를 소산시켜 원하는 공기량으로 줄이고 원래의 슬럼프로 감소시켜 속경성, 작업성, 고내구성을 확보하는 저비용 속경 성 콘크리트를 생산할 수 있다. 펌프카를 이용하여 재료를 이송 도중 공기압 와류와 낙하에 의해 교반하는 시스템으로, 펌프카에 직접 분말공급장치, 기포발생기, 에어컴프레셔 등을 연결하여 2회에 걸친 공기압 분사를 통해 재료를 교반하고 최종적으로 공기압 분사함으로써 기포를 소산 시키는 교반 시스템이다. 그림 1은 펌프카 관내 공기압 연 속식 교반 시스템의 재료 흐름 모식도이다.